1. Field of the Invention
The present invention relates to seat vertical devices or seat lifting devices for adjusting height of a seat cushion of a vehicle seat.
2. Description of the Related Art
A seat vertical device or seat lifting device for adjusting height of a seat cushion of a vehicle seat is taught, for example, by U.S. Pat. No. 6,347,778 and Japanese Laid-Open Patent Publication No. 2001-163091.
Typically, a vehicle seat comprises a seat back and a seat cushion. The seat back and the seat cushion are respectively supported by a seat back frame and a cushion frame. The cushion frame includes a pair of opposing elongated plate-shaped members or frame elements. The cushion frame thus constructed is seated on a seat slide device that are disposed on a vehicle floor. The seat slide device has a pair of slide rail assemblies that are arranged in parallel each other. The slide rail assemblies are positioned such that the distance therebetween is substantially identical to the distance between the frame elements of the cushion frame. Each of the slide rail assemblies includes an upper rail and a lower rail. The lower rail is affixed to the vehicle floor. The upper rail slidably engages the affixed lower rail.
In the known art described in U.S. Pat. No. 6,347,778, each of the frame elements of the cushion frame is linked to the upper rail of the slide rail assembly via front and rear linking mechanisms, which mechanisms constitute a seat lifting device. The front and rear linking mechanisms respectively include a front bracket and a rear bracket that are upwardly projected from the upper rail. The front linking mechanism further includes a front arm, which arm is pivotally attached to the frame element and the front bracket via pivot pins. Similarly, the rear linking mechanism further includes a rear arm, which arm is pivotally attached to the frame element and the rear bracket via pivot pins.
Further, the seat lifting device includes a drive mechanism, which drive mechanism also constitutes the seat lifting device. The drive mechanism includes a lever, an intermediate bracket upwardly project from the upper rail and a linking rod. The lever is pivotally attached to the intermediate bracket in its middle portion. One end of the linking rod is pivotally connected to the rear arm. Also, the other end of the linking rod is pivotally connected to an upper end of the lever. Further, a nut is rotatably attached to a lower end of the lever. This nut threadably engages a threaded shaft that is driven or rotated by a drive means or motor. Therefore, when the threaded shaft is rotated by the motor, the nut moves along the threaded shaft, thereby pivoting the lever around the intermediate bracket. As a result, the linking rod connected to the lever moves back and forth, thereby pivoting the rear arm. Thus, the flame element can be lifted, so that the height of the vehicle seat cushion can be adjusted.
In the known seat lifting device, the rear arm is formed with a laterally elongated slot (first slot) and a vertically elongated arcuate slot (second slot) having a plurality of concave portions arranged therealong. On the other hand, the rear arm is provided with a pivot pin that is received in the first slot and a locking pin that is received in the second slot.
According to the known seat lifting device, when an excessive forward and upward force is applied to the cushion frame via a seatbelt that is attached thereto, each of the frame elements of the cushion frame may be pulled forwardly and upwardly and moves in this direction. As a result, the rear arm rotates around the pivot pin. However, because the pivot pin is received within the elongated slot, the rear arm forwardly is shifted, thereby engaging the locking pin with one of the concave portions of the second slot. Thus, the seat lifting device is locked, thereby preventing the frame element from further moving forwardly and upwardly. As a result, the rear arm can be effectively prevented from further rotating around the pivot pin. Therefore, the drive mechanism that is linked to the rear arm can be effectively prevented from being subjected to an undesirable large force.
As will be recognized, if the seat lifting device is not locked when the excessive forward and upward force is applied to the cushion frame, the frame element cannot be prevented from moving forwardly and upwardly. Therefore, the rear arm can freely rotate around the pivot pin. As a result, a considerable force may be applied to the drive mechanism linked to the rear arm. Such a force may exert undesirable effects on the drive mechanism.